The present application is related to a vehicle inspection or measurement system configured to utilize displacement sensors on opposite sides of a vehicle inspection lane to acquire measurement data associated with various components of a vehicle as the vehicle moves through the inspection lane, and in particular, to methods and apparatus for calibration of a set of laser displacement sensors utilized during the inspection or measurement of moving vehicles.
Systems for measuring or inspecting vehicle properties, such as wheel alignment and associated parameters, are traditionally set up to obtain measurements to a high degree of accuracy under controlled conditions, such as with the vehicle disposed in a stationary location on a level floor surface or alignment lift rack. These vehicle measurement or inspection systems may require the temporary placement of various inclinometers or optical targets on the vehicle wheels, from which data is acquired to determine the various measurements. In general, vehicle wheel alignment measurement or inspection procedures require a technician to spend time preparing the vehicle for measurements, acquiring the measurements, and optionally performing adjustments necessary to correct any identified problems. Often, a vehicle brought in to a shop for other services may unknowingly be in need of an alignment service as well. However, unless the service technician and the vehicle owner are willing to spend the time required to prepare the vehicle for measurement and proceed with an alignment measurement process, alignment issues will likely remain undetected and unrepaired.
In response to the recognized need for a way to quickly identify vehicles which may require an alignment service, various quick check or dedicated inspection systems have been introduced to the market, such as the Quick Check® System from Hunter Engineering Co. of St. Louis, Mo. These systems provide an operator with the tools and procedures necessary to obtain basic measurements of important vehicle wheel alignment angles, enter vehicle identifying information (such as through a VIN barcode scan), and review vehicle diagnostic information such as battery condition, tire tread depth, and on-board diagnostic messages. If a vehicle quick check or inspection reveals a potential out-of-specification measurement or problem, it can be brought to the attention of the vehicle owner, who may then elect to proceed with a more in-depth vehicle service procedure, such as a full vehicle wheel alignment service using specialized precision equipment.
Often, vehicle quick check or inspection systems require a technician to carry out various tasks during the process, including attachment of optical targets or angle sensors to the wheels of the vehicle, manual measurement of tire tread depths, and the coupling of scanner component to vehicle data ports. In order for the technician to complete these tasks, the vehicle must be stationary for part of the time, such as for the attachment (and subsequent removal) of optical targets or angle sensors. This necessitates establishing a routine or procedure which must be followed by a technician each time a vehicle is brought into the shop for service. During busy times, or when multiple customers are waiting, a technician may not have sufficient time to carry out these routines or procedures for every vehicle, potentially failing to identify vehicles in need of additional services.
Vehicle wheel alignment systems have utilized a variety of techniques for non-contact measurement of stationary vehicle wheel assembly parameters, from which vehicle wheel alignment angles can be determined. For example, by utilizing multiple displacement measurement sensors, distances between known sensor locations and locations on a stationary vehicle wheel assembly can be measured. Processing the acquired measurements from displacement sensors observing wheels on opposite sides of an axle can identify planes parallel to the wheel assembly surfaces, from which representations of total toe and camber angles for the vehicle can be determined. In other configurations, two-dimensional images of a stationary vehicle wheel assembly are acquired, and image processing algorithms utilized to identify geometric features such as the wheel rim edge, from which a perspective analysis can be performed to determine estimates of vehicle wheel assembly spatial position and orientation. Alternatively, structured light patterns, such as multiple laser lines, or colored stripes, can be projected onto the stationary wheel assembly surface and observed by an imaging system. Deviations in the projected pattern are analyzed to generate representations of the illuminated surfaces, from which vehicle wheel assembly spatial position and orientation can be estimated. In general, these systems require the vehicle to remain stationary relative to the sensors during the measurement acquisition procedure, but some non-contact measurement systems require either the wheel assembly or the sensors be rotated in place about a stationary axis of rotation during the measurement acquisition procedure.
Some non-contact measurement systems can acquire measurements as a vehicle wheel assembly is both rotated and translated past the sensors, i.e., as the vehicle is moved past the sensors. For example, using laser displacement sensors to measure a distance between a fixed sensor and various points on vehicle wheel assemblies on opposite sides of a vehicle as a vehicle is driven at a slow speed between the sensors, enables a system to acquire measurement data along horizontal slices of the wheel assemblies, from which approximations of the wheel spatial orientations can be derived. These types of systems are highly influenced by the speed at which the vehicle travels between the sensors, the angle (straightness) of vehicle travel relative to the sensor observation axis, suspension movement, and changes in steering of the vehicle as it passes between sensors. Measurements acquired from a moving vehicle are useful to provide a vehicle service quick check or audit inspection, capable of identifying vehicles which may be in need of a further, more precise, alignment inspection and/or adjustment. However, in order to provide meaningful information, it is necessary that the measurements acquired from the moving vehicle are substantially representative of the alignment of the moving vehicle components, and do not introduce errors due to improper calibration of the associated laser displacement sensors.
Accordingly, it would be advantageous to provide a method and apparatus by which the laser displacement sensors utilized in a non-contact measurement or inspection system for a moving vehicle can be calibrated to provide displacement measurements which are sufficiently accurate to measure the alignment of vehicle components to within an acceptable tolerance of measurements acquired from a stationary vehicle using a traditional vehicle wheel alignment measurement system.
It would be further advantageous to provide, for non-contact measurement or inspection systems for a moving vehicle utilizing a plurality of laser displacement sensors, a method and apparatus by which the plurality of laser displacement sensors can be calibrated together to ensure that displacement measurements from each laser displacement sensor are accurate relative to each other to within an acceptable tolerance. Similarly, for a plurality of laser displacement sensors arrayed together in a non-contact measurement or inspection system, it would be beneficial to ensure that laser beams emitted by each sensor are optically consistent to within an acceptable tolerance for spot dispersion, illumination intensity, and other optical characteristics.